We will develop murine IgA monoclonal antibodies (mAbs), stabilized by recombinant secretory component, against Clostridium difficile toxins and other virulence factors. MAbs will be characterized by protein specificity and biological activity. IgA antibodies will be sought that protect laboratory animals upon oral administration against C. difficile-induced colonization, enteritis and death. The epitope specificity of protective IgA mAbs will be mapped using synthetic and recombinant peptides, representing selected domains of C. difficile toxins A and B. Human colonic aspirates containing IgA antibodies to C. difficile will also be tested against these peptides to determine the dominant epitopes involved in human mucosal immune responses. The results are expected to define the role of mucosal immunity in protection against C. difficile, and to identify IgA antibodies with potential as human products for passive immunization, prophylaxis and therapy of antibiotic-associated diarrhea and colitis. In addition, they will elucidate specific antigenic targets for a vaccine designed to induce active mucosal immunity against C. difficile.